JP6149641B2 - Gas sensor control device - Google Patents

Description

  The present invention relates to a gas sensor control device.

  For example, there is known a gas sensor that detects exhaust gas discharged from an in-vehicle engine and detects the NOx concentration in the exhaust gas. The gas sensor (NOx sensor) includes a pump cell and a sensor cell each having a solid electrolyte body and a pair of electrodes disposed on the solid electrolyte body, and oxygen in the exhaust gas introduced into the chamber is transferred by the pump cell. In addition to exhaust, a sensor cell that detects NOx concentration from oxygen exhausted gas has been put into practical use. In addition, as a deterioration diagnosis device for performing such deterioration diagnosis of a gas sensor, a device that forcibly switches the applied voltage to the pump cell and determines the deterioration of the gas sensor based on a change in the output of the sensor cell accompanying the switching of the applied voltage is proposed. (For example, refer to Patent Document 1). Further, in such a deterioration diagnosis device, the output of the sensor cell is corrected based on the applied voltage change amount and the sensor cell output change amount.

JP 2009-175013 A

  However, even when a certain voltage is applied to the pump cell, the current flowing through the pump cell may be an undesired amount of current, leading to a decrease in the accuracy of sensor cell deterioration diagnosis and sensor cell output correction. There is a concern that it may not be possible to perform properly. For example, in a pump cell, it is conceivable that the pump cell current (in other words, the amount of oxygen exhausted by the pump cell) changes depending on the state of deterioration or activity, which affects the residual oxygen concentration in the chamber. The sensor cell output fluctuates due to the influence on the residual oxygen concentration, and as a result, deterioration diagnosis and output correction cannot be performed properly.

  The main object of the present invention is to provide a gas sensor control device capable of realizing proper management of a gas sensor.

  Hereinafter, means for solving the above-described problems and the effects thereof will be described.

  The gas sensor control device of the present invention includes a first cell (31) having a solid electrolyte body (11, 12) and a pair of electrodes (32, 33, 36 to 38) disposed on the solid electrolyte body. And the gas sensor (10) including the second cell (34, 35), and the gas sensor discharges oxygen in the gas to be detected introduced into the gas chamber (14, 16) by the first cell. The second cell detects the concentration of the specific component from the gas after the oxygen is exhausted. An oxygen discharge amount changing means for temporarily changing the amount of oxygen discharge by the first cell, and an actual oxygen discharge change amount in a state where the oxygen discharge amount is changed by the oxygen discharge amount changing means. First calculation means for calculating an emission amount; second calculation means for calculating an amount of output change caused by a change in oxygen discharge amount by the oxygen discharge amount change means in the second cell; and the first calculation means. Correction of the concentration of the specific component detected by the second cell based on the actual discharge amount calculated by the second calculation unit and the output change amount of the second cell calculated by the second calculation unit; and And main control means for performing at least one of the deterioration determinations of the two cells.

  In the above configuration, when the amount of oxygen discharge by the first cell (pump cell) is changed, the actual discharge amount (actual oxygen discharge change amount) caused by the change is calculated and the second cell (sensor cell). , The output change amount in the monitor cell) is calculated. In this case, even if the actual oxygen discharge amount (oxygen pumping amount) in response to the oxygen discharge instruction changes according to the deterioration or active state in the first cell, how much oxygen discharge actually occurs. Can be monitored. Then, based on the actual discharge amount in the first cell and the output change amount in the second cell, the correction of the concentration of the specific component detected by the second cell and the deterioration determination of the second cell are performed. The accuracy of density calculation and deterioration determination can be improved. As a result, proper management of the gas sensor can be realized.

The block diagram which shows the element internal structure of a NOx sensor, and a sensor control circuit. The block diagram which shows the outline | summary of an engine system. The figure which shows the output characteristic of a NOx sensor. The figure which shows the detail of the output characteristic of a pump cell. The flowchart which shows the process sequence of correction value calculation of a sensor output. The time chart for demonstrating more concretely about correction value calculation. The flowchart which shows the deterioration determination process of a sensor cell and a monitor cell. The figure which shows the relationship between NOx density | concentration and Vp change amount.

  DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment embodying a gas sensor control device of the present invention will be described with reference to the drawings. In the present embodiment, a NOx concentration detection device that uses a NOx sensor provided in an exhaust pipe of an in-vehicle engine (internal combustion engine) and detects the NOx concentration in the exhaust based on the output of the NOx sensor will be described. A configuration shown in FIG. 2 is assumed as an engine system to which the NOx concentration detection device is applied.

  In FIG. 2, an engine 50 is a multi-cylinder diesel engine, for example, and has a plurality of injectors 51 for injecting fuel. An exhaust purification device 53 is provided in the exhaust pipe 52 of the engine 50. The exhaust purification device 53 is a NOx purification catalyst such as a NOx occlusion reduction type catalyst or an ammonia selective reduction catalyst, and NOx and the like are purified when the exhaust passes through the exhaust purification device 53. Further, on the downstream side of the exhaust purification device 53, a NOx sensor 10 for detecting the NOx concentration in the exhaust is provided.

  The ECU 60 is an electronic control device including a known microcomputer including a CPU, various memories, and the like. The ECU 60 receives a detection signal from the NOx sensor 10 and also detects a rotation speed of the engine 50. A detection signal is input from 61 or a load sensor 62 that detects an engine load such as an accelerator opening. The ECU 60 performs fuel injection control of the injector 51, deterioration determination of the exhaust purification device 53, and the like based on these detection signals and the like.

  Next, the sensor element 10a constituting the NOx sensor 10 will be described with reference to FIG. The sensor element 10a has a so-called laminated structure, and its internal structure is shown in FIG. The horizontal direction in the figure corresponds to the longitudinal direction of the sensor element 10a. The right side of the figure is the element base end side (exhaust pipe attachment site side), and the left side of the figure is the element tip side. The sensor element 10a has a so-called three-cell structure including a pump cell, a sensor cell, and a monitor cell, and each cell is stacked and configured. Since the monitor cell has a function of discharging oxygen in the gas like the pump cell, the monitor cell may be referred to as an auxiliary pump cell or a second pump cell.

  In the sensor element 10a, the solid electrolyte bodies 11 and 12 made of an oxygen ion conductive material such as zirconia are formed in a sheet shape, and are stacked at a predetermined interval above and below the figure via spacers 13 made of an insulating material such as alumina. ing. Among these, an exhaust inlet 11a is formed in the solid electrolyte body 11 on the upper side of the figure, and exhaust around the sensor element is introduced into the first chamber 14 through the exhaust inlet 11a. The first chamber 14 communicates with the second chamber 16 via the throttle unit 15. Both chambers 14 and 16 correspond to gas chambers. On the upper surface side of the solid electrolyte body 11 in the figure, a porous diffusion layer 17 for taking in and out the exhaust gas with a predetermined diffusion resistance is provided, and an insulating layer 19 for partitioning the air passage 18 is provided. .

  Further, an insulating layer 21 made of alumina or the like is provided on the lower surface side of the solid electrolyte body 12 in the figure, and an atmospheric passage 22 is formed by the insulating layer 21. A heater (heating element) 23 is embedded in the insulating layer 21 for heating the entire sensor. In this case, the pump 23, the monitor cell 34, and the sensor cell 35 are heated by the heater 23, and activation of each of these cells 31, 34, 35 is promoted. The heater 23 generates thermal energy by power supply from a battery power source (not shown).

  The solid electrolyte body 12 on the lower side of the figure is provided with a pump cell 31 so as to face the first chamber 14. The pump cell 31 takes in and out oxygen in the exhaust gas introduced into the first chamber 14. The residual oxygen concentration in the chamber 14 is adjusted to a predetermined concentration. The pump cell 31 has a pair of upper and lower electrodes 32 and 33 provided with the solid electrolyte body 12 sandwiched therebetween, and in particular, the electrode 32 on the first chamber 14 side is a NOx inert electrode (an electrode that is difficult to decompose NOx). Yes. The pump cell 31 decomposes oxygen present in the first chamber 14 in a state where a voltage is applied between the electrodes 32 and 33 and discharges it from the electrode 33 to the atmosphere passage 22 side.

  Further, a monitor cell 34 and a sensor cell 35 are provided in the upper solid electrolyte body 11 in the drawing so as to face the second chamber 16. After the surplus oxygen is discharged by the pump cell 31 described above, the monitor cell 34 generates a current output in accordance with the electromotive force or voltage application according to the residual oxygen concentration in the second chamber 16. The sensor cell 35 detects the NOx concentration from the gas in the second chamber 16. In the present embodiment, the pump cell 31 corresponds to a “first cell”, and the monitor cell 34 and the sensor cell 35 correspond to a “second cell”. The monitor cell 34 detects the residual oxygen concentration in the second chamber 16 as “specific component concentration”, and the sensor cell 35 detects the NOx concentration in the second chamber 16 as “specific component concentration”.

  The monitor cell 34 and the sensor cell 35 are arranged side by side at positions close to each other, and have a configuration in which electrodes 36 and 37 are provided on the second chamber 16 side and a common electrode 38 is provided on the atmosphere passage 18 side. That is, the monitor cell 34 is constituted by the solid electrolyte body 11, the electrode 36 and the common electrode 38 disposed so as to face each other, and the sensor cell 35 is similarly configured to face the solid electrolyte body 11 and the electrode 37 disposed so as to face it. And the common electrode 38. The electrode 36 (electrode on the second chamber 16 side) of the monitor cell 34 is made of a noble metal such as Au—Pt that is inactive to NOx, whereas the electrode 37 (electrode on the second chamber 16 side) of the sensor cell 35 is active for NOx. It consists of noble metals such as platinum Pt and rhodium Rh. For convenience, in the drawing, the monitor cell 34 and the sensor cell 35 are shown side by side with respect to the exhaust flow direction (left and right direction in the figure), but in actuality, these cells 34 and 35 are located at the same position with respect to the exhaust flow direction. It is arranged to become.

  Here, the pump cell 31, the monitor cell 34, and the sensor cell 35 are provided side by side in the longitudinal direction of the sensor element 10a, the pump cell 31 is provided at the distal end side of the sensor element 10a, and the base end side (exhaust pipe attachment side) ) Are provided with a monitor cell 34 and a sensor cell 35.

  In the sensor element 10a configured as described above, the exhaust gas is introduced into the first chamber 14 through the porous diffusion layer 17 and the exhaust gas inlet 11a. When this exhaust gas passes through the vicinity of the pump cell 31, a decomposition reaction occurs by applying a pump cell voltage Vp between the pump cell electrodes 32 and 33, and the exhaust cell passes through the pump cell 31 according to the oxygen concentration in the first chamber 14. Oxygen is taken in and out. At this time, since the electrode 32 on the first chamber 14 side is a NOx inactive electrode, NOx in the exhaust gas is not decomposed in the pump cell 31, but only oxygen is decomposed and discharged from the electrode 33 to the atmospheric passage 22. By the action of the pump cell 31, the inside of the first chamber 14 is maintained in a predetermined low oxygen concentration state.

  The gas that has passed through the vicinity of the pump cell 31 (the gas after the oxygen concentration adjustment) flows into the second chamber 16, and the monitor cell 34 generates an output corresponding to the residual oxygen concentration in the gas. The output of the monitor cell 34 is detected as a monitor cell current Im when a predetermined monitor cell voltage Vm is applied between the monitor cell electrodes 36 and 38. Further, when a predetermined sensor cell voltage Vs is applied between the sensor cell electrodes 37 and 38, NOx in the gas is reduced and decomposed, and oxygen generated at that time is discharged from the electrode 38 to the atmospheric passage 18. At this time, the NOx concentration in the exhaust gas is detected by the current (sensor cell current Is) flowing through the sensor cell 35.

  The sensor control circuit 40 includes a microcomputer 41 that is a main body for sensor control, and a circuit unit having a voltage application unit, a current detection unit, and the like. The microcomputer 41 and the circuit unit are used to connect the electrodes 32 and 33 of the pump cell 31. The pump cell voltage Vp applied to the monitor cell 34, the monitor cell voltage Vm applied between the electrodes 36 and 38 of the monitor cell 34, and the sensor cell voltage Vs applied between the electrodes 37 and 38 of the sensor cell 35 are controlled. The detected values of the pump cell current Ip, the monitor cell current Im, and the sensor cell current Is are sequentially input to the microcomputer 41, and the microcomputer 41 calculates the oxygen concentration and NOx concentration in the exhaust based on these detected values. For example, the microcomputer 41 may be provided in the ECU 60 of FIG.

  In the microcomputer 41, the current detection value of each cell is input via an A / D converter (not shown). In this case, a current is detected within a current detection range (corresponding to a concentration detection range) determined for each cell, and the current detection value is converted within the voltage conversion range (for example, 0 to 5 V) of the A / D converter. Are taken into the microcomputer 41.

  Next, output characteristics of the NOx sensor 10 will be described with reference to FIG. 3A shows the output characteristic (VI characteristic) of the pump cell 31, and FIG. 3B shows the output characteristic (VI characteristic) of the sensor cell 35. FIG. The horizontal axis of FIG. 3A is the pump cell voltage Vp, and the vertical axis is the pump cell current Ip. In FIG. 3B, the horizontal axis represents the sensor cell voltage Vs, and the vertical axis represents the sensor cell current Is.

  In FIG. 3A, a flat portion substantially parallel to the voltage axis (horizontal axis) is a limit current region for specifying the pump cell current Ip, and the increase / decrease of the pump cell current Ip corresponds to the oxygen concentration in the exhaust gas. . That is, the pump cell current Ip increases as the oxygen concentration in the exhaust gas increases, and the pump cell current Ip decreases as the oxygen concentration in the exhaust gas decreases. The limit current region shifts to the higher voltage side as the oxygen concentration increases, and accordingly, the applied voltage characteristic (applied voltage line Vp0) for determining the pump cell voltage Vp is shifted to the higher voltage side. Yes. Further, the slope portion on the lower voltage side than the limit current region is the resistance dominant region. The slope of the resistance dominating region depends on the element temperature, and the slope is smaller as the element temperature is lower.

  In FIG. 3B, the flat portion substantially parallel to the voltage axis (horizontal axis) is a limit current region for specifying the sensor cell current Is, and the increase / decrease in the sensor cell current Is corresponds to the NOx concentration in the exhaust gas. ing. That is, the sensor cell current Is increases as the NOx concentration in the exhaust gas increases, and the sensor cell current Is decreases as the NOx concentration in the exhaust gas decreases. The sensor cell voltage Vs is set at a predetermined value Vs0 that enables detection of a sensor cell current Is corresponding to a predetermined NOx concentration in the limit current region. Similar to the pump cell output characteristics, the slope portion on the lower voltage side than the limit current region is the resistance dominant region, and the slope becomes smaller as the element temperature is lower.

  The current output from the pump cell 31 and the current output from the sensor cell 35 are different in order. The pump cell 31 outputs the pump cell current Ip in the mA order, and the sensor cell 35 outputs the sensor cell current Is in the μA order. The maximum detection range of the NOx concentration is 3000 ppm.

  In the sensor control circuit 40 of the present embodiment, the amount of oxygen discharge is temporarily forcibly changed by the pump cell 31, and the sensitivity of the sensor cell 35 and the monitor cell 34 is based on the change amount of the sensor cell output and the change amount of the monitor cell output at that time. The amendment is to be implemented. That is, in the NOx sensor 10, when the oxygen discharge amount (oxygen pumping amount) in the pump cell 31 is forcibly changed, the oxygen concentration after oxygen discharge (oxygen concentration in the second chamber 16) changes accordingly, and the oxygen A change in sensor cell output and a change in monitor cell output corresponding to the amount of change in density occur. However, if an error in sensitivity occurs due to individual differences or deterioration in the sensor cell 35 or the monitor cell 34, each change amount of the sensor cell output / monitor cell output with respect to the change in the oxygen concentration differs from the original change amount. . Therefore, each change amount of the sensor cell output / monitor cell output when the oxygen pumping amount is changed is obtained, and the sensor cell output (corresponding to the NOx concentration) and the monitor cell output (corresponding to the residual oxygen concentration) based on the output change amount. Perform the correction.

  In the present embodiment, in particular, in order to suppress a decrease in accuracy of the sensor detection signal due to variations in the oxygen discharge amount in the pump cell 31, the actual oxygen pumping amount (actual discharge amount) is obtained after instructing the change of the oxygen pumping amount. The correction values of the sensor cell output and the monitor cell output are calculated using the actual oxygen pumping amount. Specifically, when a change in the pump cell voltage Vp is instructed, a pump cell current change amount ΔIp (hereinafter also referred to as a pump cell output change amount ΔIp) corresponding to an actual oxygen pumping amount based on the pump cell current Ip before and after the instruction. ) Is calculated. Then, each correction value of the sensor cell output and the monitor cell output is calculated using the pump cell output change amount ΔIp.

  Here, the detail of the output characteristic of the pump cell 31 is demonstrated using FIG. In the output characteristics shown in FIG. 4, the limit current region is between A and B, and this limit current region is a region where a substantially constant pump cell current Ip is output with respect to the pump cell voltage Vp on the horizontal axis. However, in detail, there is a slope in the limit current region, and the pump cell current Ip changes when the pump cell voltage Vp is changed. For example, when the pump cell voltage Vp is changed from Vp1 to Vp2, the pump cell current Ip changes from Ip1 to Ip2. In this case, the pump cell current Ip is reduced by (Ip1-Ip2), so that the oxygen discharge amount in the pump cell 31 is reduced and the residual oxygen concentration in the second chamber 16 of the NOx sensor 10 is increased. Accordingly, the sensor cell output and the monitor cell output change accordingly. The pump cell current Ip can be regarded as the oxygen discharge capacity in the pump cell 31, and it can be said that the oxygen discharge capacity is lowered due to the decrease in Ip.

  Further, in the output characteristics of the pump cell 31, it is considered that there is a difference in the slope of the limit current region, and when this difference occurs, the change amount of the pump cell current Ip (actual oxygen discharge amount with respect to the instruction of oxygen discharge) is generated. The influence is exerted, and consequently the accuracy of correction value calculation is reduced. Possible causes of the difference in the slope of the limit current region include individual differences of the pump cells 31, changes with time such as deterioration, and differences in the active state. In this respect, as described above, the pump cell output change amount ΔIp is calculated from the pump cell current Ip before and after the change of Vp, and the output change amounts ΔIs and ΔIm of the sensor cell 35 and the monitor cell 34 before and after the change of Vp are calculated, and ΔIp, ΔIs, ΔIm are calculated. Are used to calculate the output correction values of the sensor cell 35 and the monitor cell 34, respectively. Therefore, even if there is a difference in the slope of the limit current region, the correction value can be calculated in a state that reflects the difference.

  In the present embodiment, the sensor cell 35 detects a maximum NOx concentration of about 3000 ppm, and it is desirable that the oxygen concentration be changed within the detection range. Therefore, it is preferable that the pump cell voltage Vp is changed within a range that falls within the limit current region in the output characteristics of the pump cell 31.

  FIG. 5 is a flowchart showing a processing procedure for calculating the correction value of the sensor output, and this processing is repeatedly performed by the microcomputer 41 at a predetermined cycle.

In FIG. 5, in step S <b> 11, it is determined whether or not an execution condition for calculating a correction value of the sensor output (each output correction value of the sensor cell 35 and the monitor cell 34) is satisfied. The implementation conditions include
The NOx sensor 10 is in a predetermined active state,
The engine 50 is in a fuel cut state,
-The specified time (waiting time for sensor output stabilization) has elapsed since the start of fuel cut.
The pump cell 31 is normal,
If all of these are satisfied, it is determined that the execution condition for calculating the correction value is satisfied. The determination that the pump cell 31 is normal may be performed by an arbitrary method. For example, in a state where the oxygen concentration is known (for example, an atmospheric state), the pump cell current Ip is a predetermined value (for example, an atmospheric equivalent value). The normality determination may be performed based on whether or not.

  Further, in step S12, it is determined whether or not a correction value has not been calculated after the ignition switch (power switch) of the vehicle is turned on. If any of steps S11 and S12 is NO, the process is terminated as it is. If both steps S11 and S12 are YES, the process proceeds to subsequent step S13.

  In step S13, it is determined whether or not an instruction to change the pump cell voltage Vp has been issued. If it is before the instruction to change Vp, the process proceeds to step S14, and the pump cell current Ip1, sensor cell current Is1, and monitor cell current Im1 before the change of Vp are read. In the subsequent step S15, an instruction to change the pump cell voltage Vp is executed. At this time, the change amount of the pump cell voltage Vp causes a decrease change of the oxygen concentration corresponding to 3000 ppm in the NOx concentration. However, the change amount of the pump cell voltage Vp may be one that causes a change in decrease in oxygen concentration that is less than 3000 ppm, and may be any change that causes a change in decrease in oxygen concentration equivalent to 2000 to 3000 ppm, for example.

  If it is after the instruction to change Vp, the process proceeds to step S16, and it is determined whether or not a predetermined time (convergence time of each current) has elapsed after the change of the pump cell voltage Vp. In this case, if a predetermined time has elapsed after the Vp change, the process proceeds to step S17, and the pump cell current Ip2, the sensor cell current Is2, and the monitor cell current Im2 after the Vp change are read. In the subsequent step S18, output changes ΔIp, ΔIs, and ΔIm before and after the Vp change are calculated for the pump cell 31, the sensor cell 35, and the monitor cell 34, respectively (ΔIp = Ip1-Ip2, ΔIs = Is2-Is1, ΔIm = Im2-Im1). . In this case, the output change amount ΔIp of the pump cell 31 is calculated as a decrease amount of the pump cell current Ip, and the output change amounts ΔIs and ΔIm of the sensor cell 35 and the monitor cell 34 are calculated as increase amounts of the sensor cell current Is and the monitor cell current Im.

  Thereafter, in step S19, output sensitivity values Ks and Km of the sensor cell 35 and the monitor cell 34 are calculated by dividing the output change amounts ΔIs and ΔIm of the sensor cell 35 and the monitor cell 34 by the output change amounts ΔIp of the pump cell 31 (Ks). = ΔIs / ΔIp, Km = ΔIm / ΔIp).

  Thereafter, in step S20, the output sensitivity values Ks and Km of the cells 35 and 34 calculated in step S19 and the sensitivity reference values Rs and Rm of the cells 35 and 34 are used to output the cells 35 and 34. Correction values Hs and Hm are calculated (Hs = Ks / Rs, Hm = Km / Rm). The sensitivity reference values Rs and Rm are determined according to the amount of change in Vp, and are determined in advance as sensitivity values in an initial state in which no deterioration or the like has occurred.

  Thereafter, in step S21, the calculated output correction values Hs and Hm are stored in the backup memory as learning values. The backup memory may be an EEPROM (registered trademark) provided in the ECU 60, for example. Thereafter, in step S22, the pump cell voltage Vp is returned to the voltage value before the change.

The output correction values Hs and Hm (learned values) are read as necessary during normal control, and the sensor cell output and the monitor cell output are corrected by the output correction values Hs and Hm. That is, in this case, the NOx concentration and the residual oxygen concentration are corrected by the output correction values Hs and Hm. The sensor cell output and the monitor cell output may be converted into physical values by the following equations.
Sensor cell output physical value = sensor cell output × Gs × Hs
Monitor cell output physical value = monitor cell output x Gm x Hm
Gs and Gm are conversion coefficients for converting the sensor cell output and the monitor cell output into physical values, respectively.

  FIG. 6 is a time chart for more specifically explaining correction value calculation.

  In FIG. 6, the air / fuel ratio is a predetermined air / fuel ratio (lean air / fuel ratio) before the timing t1, the pump cell 31 outputs a pump cell current Ip corresponding to the oxygen concentration in the first chamber 14, and the sensor cell 35 in the second chamber 16. The sensor cell current Is corresponding to the NOx concentration and oxygen concentration of the second chamber 16 is output, and the monitor cell 34 outputs the monitor cell current Im corresponding to the oxygen concentration in the second chamber 16.

  At timing t1, the engine 50 is in a fuel cut state, and the air-fuel ratio shifts to the lean side (atmosphere side) at once. As a result, the pump cell current Ip increases to an atmospheric equivalent value. Further, when NOx in the exhaust gas decreases (substantially becomes zero), Is decreases, and Is = Im is obtained. That is, it is possible to acquire the sensor cell current Is that is not affected by the NOx concentration during the fuel cut. In FIG. 6, the pump cell voltage Vp is constant even when the air-fuel ratio shifts to the atmosphere side. However, as shown in FIG. 3A, the pump cell voltage Vp can be changed according to the air-fuel ratio. .

  Thereafter, at a timing t2 when a predetermined time has elapsed from the start of fuel cut, a change to the decrease side of the pump cell voltage Vp is instructed, and accordingly, the respective currents Ip, Is, Im are changed. Then, output variations ΔIp, ΔIs, ΔIm are calculated from the currents Ip, Is, Im before and after the change of Vp. Further, the output sensitivity values Ks and Km and the output correction values Hs and Hm of the sensor cell 35 and the monitor cell 34 are calculated using these output change amounts ΔIp, ΔIs, ΔIm and the like. At this time, since the fuel is being cut and the detection of NOx is not performed, it is possible to change the sensor cell current Is using the NOx detection range as much as possible, and output sensitivity values Ks, Km. In addition, the calculation accuracy of the output correction values Hs and Hm can be improved.

  Thereafter, at timing t3, the fuel cut is finished, and the pump cell voltage Vp is returned to the voltage value before the change.

  Further, if the output change amounts ΔIp, ΔIs, ΔIm before and after the Vp change instruction are used, it is possible to determine the deterioration of the sensor cell 35 and the monitor cell 34. Therefore, in this embodiment, the deterioration determination of the sensor cell 35 and the monitor cell 34 is performed using the output sensitivity values Ks and Km calculated based on the output change amounts ΔIp, ΔIs, and ΔIm of each cell. FIG. 7 is a flowchart showing the deterioration determination process of the sensor cell 35 and the monitor cell 34. This process is repeatedly performed by the microcomputer 41 at a predetermined cycle.

  In FIG. 7, in step S31, output sensitivity values Ks and Km of the sensor cell 35 and the monitor cell 34 are read. The output sensitivity values Ks and Km are calculated based on the output change amounts ΔIp, ΔIs, and ΔIm of each cell using the method already described with reference to FIG. 5, and are not described here. Thereafter, in step S32, it is determined whether or not the output sensitivity value Ks of the sensor cell 35 is an abnormal value. And if it is an abnormal value, it will progress to step S33 and will determine that the sensor cell 35 has deteriorated. Here, a normal range is determined in advance for the output sensitivity value Ks, and if the output sensitivity value Ks is equal to or higher than the upper limit or lower than the lower limit of the normal range, an abnormal determination is made as an abnormal value (described later). The same applies to the output sensitivity value Km).

  In step S34, it is determined whether or not the output sensitivity value Km of the monitor cell 34 is an abnormal value. And if it is an abnormal value, it will progress to step S35 and will determine that the monitor cell 34 has deteriorated.

  In addition to using the output sensitivity values Ks and Km as abnormality determination parameters, the output change amounts ΔIs and ΔIm may be used as abnormality determination parameters, or the output correction values Hs and Hm may be used as abnormality determination parameters. Is possible.

  According to the embodiment described in detail above, the following excellent effects can be obtained.

  When the amount of oxygen discharge by the pump cell 31 (first cell) is changed, the output change amount ΔIp (corresponding to the actual discharge amount) generated with the change is calculated, and the sensor cell 35 and the monitor cell 34 (second cell). The output change amounts ΔIs and ΔIm are calculated, and output correction and deterioration determination of the sensor cell 35 and the monitor cell 34 are performed based on the output change amounts ΔIp, ΔIs, and ΔIm of each cell. In this case, it is possible to perform correction value calculation (concentration calculation) and deterioration determination after monitoring how much oxygen discharge actually occurs in response to the oxygen discharge instruction, and the accuracy can be improved. As a result, proper management of the NOx sensor 10 can be realized.

  In calculating the output correction value, the pump cell voltage Vp is temporarily changed on condition that the engine 50 is in a fuel cut state. In this case, the NOx concentration is zero in the fuel cut state of the engine 50, and the oxygen emission amount can be changed using the entire range of NOx concentration detection in the sensor cell 35. Specifically, when the upper limit of NOx concentration detection is 3000 ppm, oxygen pumping in an amount corresponding to the upper limit of concentration is possible. Therefore, the reliability of output correction can be improved. In addition, the reliability of the deterioration determination can be similarly increased.

  Also, in the fuel cut state, unlike the states other than the fuel cut, appropriate output correction and deterioration determination can be performed regardless of the purification performance of the exhaust purification device 53 (catalyst). That is, in the configuration in which the NOx sensor 10 is provided on the downstream side of the exhaust purification device 53 as in the present embodiment, there may be a difference in the amount of NOx that flows downstream depending on the purification status of the exhaust purification device 53. In the fuel cut state, output correction and deterioration determination can be appropriately performed without depending on the purification state of the exhaust purification device 53. In addition, there is an advantage that output correction and deterioration determination can be performed at any time regardless of the state of the exhaust purification catalyst (for example, active / inactive state).

  Further, the fuel cut state is a state in which the NOx concentration is kept constant, and it is possible to avoid the disadvantage that the output correction value is erroneously calculated or the deterioration is erroneously determined due to the fluctuation of the NOx concentration.

  On the condition that the pump cell 31 is normal, the calculation of the output correction values and the deterioration determination are performed, including the calculation of each output change amount ΔIp, ΔIs, ΔIm. Can increase the sex.

(Other embodiments)
You may change the said embodiment as follows, for example.

  In the above embodiment, when calculating the output correction value, the pump cell voltage Vp is temporarily changed on condition that the engine 50 is in the fuel cut state. Alternatively, the pump cell voltage Vp may be temporarily changed on condition that the NOx concentration is less than a predetermined value (a relatively low state). In this case, the output correction value may be calculated in a situation where the fluctuation of the NOx concentration is unlikely to occur. For example, the output correction value may be calculated when the exhaust purification catalyst provided on the upstream side of the NOx sensor 10 is in an active state and the engine 50 is in an idle state.

  In a state where the NOx concentration is relatively low, the sensor cell current Is before the change of Vp is relatively small, and the possible increase in current with respect to the upper limit value of the sensor cell current Is is relatively large. That is, the range of forced change of the sensor cell current Is can be made relatively large. Therefore, the reliability of output correction can also be improved.

  When calculating the output correction value, when the pump cell voltage Vp is temporarily forcibly changed, the Vp change amount (oxygen discharge amount) may be variably set according to the respective NOx concentration. In this case, as shown in FIG. 8, for example, the smaller the NOx concentration (that is, the sensor cell current Is before the Vp change) is, the larger the Vp change amount is. Conversely, the larger the NOx concentration is, the smaller the Vp change amount is. Note that the Vp change amount can be variably set based on the residual oxygen concentration (that is, the monitor cell current Im before the Vp change). In such a case, the Vp change amount may be increased as the residual oxygen concentration is decreased. .

  In this configuration, when the output range of the sensor cell 35 or the monitor cell 34 is limited, the maximum output change can be caused while keeping the sensor cell output and the monitor cell output after the Vp change within a predetermined output range. it can. Thereby, the precision of output correction and deterioration determination can be improved.

  In the above embodiment, the correction value calculation and the deterioration determination are performed only once after the power switch of the vehicle is turned on, but instead, this may be performed repeatedly every time a predetermined condition is satisfied. For example, the correction value calculation and the deterioration determination may be performed every predetermined time, every predetermined traveling distance, and every time the fuel cut state is entered.

  In the above embodiment, the calculation of the output correction value and the deterioration determination are performed for both the sensor cell 35 and the monitor cell 34 of the NOx sensor 10, but instead, either one of the sensor cell 35 or the monitor cell 34 is used. It may be configured to calculate the output correction value and determine the deterioration. Moreover, the structure which implements only any one of calculation of an output correction value and deterioration determination may be sufficient.

  In the above embodiment, when the pump cell voltage Vp is temporarily changed when calculating the output correction value, the configuration in which the pump cell voltage Vp is changed to the decreasing side (the side where the oxygen emission amount is reduced) is exemplified. Thus, the pump cell voltage Vp may be changed to the increase side (the side where the oxygen discharge amount increases).

  The configuration of the NOx sensor 10 may be different from the configuration shown in FIG. For example, instead of the configuration in which the exhaust gas is introduced into the first chamber 14 via the exhaust gas inlet 11a provided in the solid electrolyte body 11, a diffusion resistance layer is provided between the solid electrolyte bodies 11 and 12 arranged opposite to each other ( For example, a part of the spacer 13 may be a diffusion resistance layer), and the exhaust gas may be introduced into the first chamber 14 through the diffusion resistance layer. In addition, instead of a configuration in which the first chamber 14 and the second chamber 16 are provided as gas chambers and they are communicated with each other via the throttle portion 15, the chambers 14 and 16 are provided as one gas having no throttle portion. You may comprise as a chamber.

  In the above embodiment, the sensor element of the NOx sensor 10 is a sensor element having a so-called three-cell structure including a pump cell, a sensor cell, and a monitor cell. However, this may be changed. For example, a sensor element having a so-called two-cell structure composed of a pump cell and a sensor cell is applied. In this case, the sensor cell corresponds to the second cell. When a monitor cell is used, the monitor cell may be an electromotive force cell that outputs an electromotive force.

  The specific component to be detected may be other than oxygen (residual oxygen) or NOx. For example, a gas sensor that uses HC or CO in the exhaust as a detection target (specific component) may be used. In this case, surplus oxygen in the exhaust is discharged by the pump cell, and HC and CO are decomposed from the gas after the surplus oxygen is discharged by the sensor cell to detect the HC concentration and the CO concentration. In addition, the concentration of ammonia in the gas to be detected may be detected.

  -It can also be embodied as a sensor control device applied to a gas sensor provided in an intake passage of an engine or a gas sensor used in other types of engines such as a gasoline engine in addition to a diesel engine. The gas sensor may be one that detects gas other than exhaust or is used for purposes other than automobiles.

  DESCRIPTION OF SYMBOLS 10 ... NOx sensor (gas sensor), 11, 12 ... Solid electrolyte body, 14, 16 ... Chamber (gas chamber), 31 ... Pump cell (1st cell), 34 ... Monitor cell (2nd cell), 35 ... Sensor cell (2nd Cell), 32, 33, 36 to 38 ... electrodes, 40 ... sensor control circuit (oxygen discharge amount changing means, first calculating means, second calculating means, main control means).

Claims (8)

A first cell (31) and a second cell (34, 35) each having a solid electrolyte body (11, 12) and a pair of electrodes (32, 33, 36-38) disposed on the solid electrolyte body. The gas sensor discharges oxygen in the gas to be detected introduced into the gas chamber (14, 16) by the first cell and discharges oxygen by the second cell. A gas sensor control device (40) for detecting the concentration of a specific component from a later gas,
Oxygen discharge amount changing means for temporarily changing the amount of oxygen discharge by the first cell;
First calculating means for calculating an actual discharge amount that is a change amount of actual oxygen discharge in a state where the oxygen discharge amount is changed by the oxygen discharge amount changing means;
Second calculation means for calculating the amount of output change caused by the change in oxygen discharge amount by the oxygen discharge amount change means in the second cell;
Based on the actual discharge amount calculated by the first calculation unit and the output change amount of the second cell calculated by the second calculation unit, the concentration of the specific component detected by the second cell Main control means for performing at least one of correction and deterioration determination of the second cell;
A gas sensor control device comprising: The oxygen discharge amount changing means is for temporarily reducing the amount of oxygen discharge by the first cell,
The first calculation means calculates an actual oxygen emission reduction amount as the actual emission amount when the oxygen emission reduction by the first cell is performed,
The second calculation means calculates an increase in output change caused by a decrease in the amount of oxygen discharged by the first cell in the second cell,
The main control means, based on the actual amount of decrease in oxygen emission calculated by the first calculation means and the increase in output change of the second cell calculated by the second calculation means, The gas sensor control device according to claim 1, wherein at least one of correction and determination of deterioration is performed. A determination means for determining that the concentration of the specific component is not more than a predetermined value for the gas to be detected;
3. The oxygen discharge amount changing unit according to claim 2, wherein, when the determination unit determines that the concentration of the specific component is equal to or lower than a predetermined value, the oxygen discharge amount changing unit temporarily decreases the amount of oxygen discharge by the first cell. Gas sensor control device. The gas sensor is a gas sensor control device that is an exhaust sensor that detects the concentration of a specific component in the exhaust gas with the exhaust gas discharged from the internal combustion engine (50) as a detection target,
The determination means determines that the concentration of the specific component is not more than a predetermined value when a fuel cut is performed in the internal combustion engine,
The gas sensor control device according to claim 3, wherein the oxygen discharge amount changing means temporarily reduces the amount of oxygen discharge by the first cell in a state where a fuel cut is performed in the internal combustion engine. The gas sensor is a NOx sensor (10) that detects the concentration of NOx in the exhaust gas,
The gas sensor control device according to claim 4, wherein the oxygen discharge amount changing means discharges oxygen corresponding to 2000 to 3000 ppm of the NOx concentration by the first cell.   2. The means for variably setting the oxygen discharge amount according to the concentration of the specific component before the change of the oxygen discharge amount when the oxygen discharge amount is changed by the oxygen discharge amount changing means. The gas sensor control apparatus as described in any one of thru | or 5.   The said 2nd cell is a sensor cell (35) which detects the density | concentration of components other than oxygen as the density | concentration of the said specific component from the gas after oxygen discharge | emission by the said 1st cell. The gas sensor control device described.   The said 2nd cell is a monitor cell (34) which detects the residual oxygen concentration in the said gas chamber as a density | concentration of the said specific component from the gas after oxygen discharge | emission by the said 1st cell. The gas sensor control apparatus according to 1.

Images